1. Field of the Invention
The present invention relates to an X-ray radiographing apparatus that detects X-rays passing through a subject and thereby obtains image information of the subject.
2. Description of the Related Art
As disclosed in Japanese Patent Laid-Open No. 2005-211226 and Japanese Patent No. 03388139, an X-ray radiographing apparatus includes an X-ray generator that emits X-rays, and an image receptor that houses an X-ray detector that detects X-rays. The X-ray generator and the image receptor are disposed opposite each other with a subject therebetween. By detecting X-rays passing through the subject, image information is obtained.
With the recent development of digital technologies, X-ray detectors using various image pickup devices that convert X-ray information into an electrical signal are making a significant progress, and digital radiographing apparatuses are becoming popular. Digital radiographing apparatuses are beginning to be introduced into many facilities, as a substitute for analogue radiographing apparatuses using a conventional film-screen method using a fluorescent member and a photosensitive film.
A solid-state flat detector, which is a typical digital X-ray detector, includes pixels and X-ray detecting elements that are thin-film transistors (TFTs). The pixels and the X-ray detecting elements are arranged in a two-dimensional array. X-rays incident on a pixel are converted into visible light by a fluorescent member. An electrical charge according to the visible light is generated by a photodiode. This electrical charge is temporarily stored in a capacitor. This stored electrical charge is read out pixel by pixel for each line, and is output as image information.
Since this image information is an electrical signal, digital radiographing apparatuses can handle not only a still image but also a moving image or a three-dimensional image information reconstructed by a computer from a plurality of projection images, and can be used to radiograph various areas of body and in various diagnosis fields.
FIG. 12 is a circuit configuration block diagram of such an X-ray radiographing apparatus. By operating an operating portion 1, a radiographing start command is output. Controlled by a control unit 2, an X-ray generator 3 emits an appropriate dose of X-rays. At the same time, the control unit 2 transmits a detection start command to an image receptor 4. The image receptor 4 detects X-rays emitted from the X-ray generator 3 and converts them into an electrical signal. This electrical signal is input into an image processor 5, undergoes appropriate image processing, and is then transferred to a display 6 and displayed as a visible image.
FIG. 13 schematically shows an X-ray radiographing apparatus for taking still images of the chest and abdomen of a subject M in the upright position. A support 11 is set upright in front of the subject M. An image receptor 4 is attached to the support 11 using a coupler 12 so as to be movable in the vertical direction. A case 13 of the image receptor 4 houses an X-ray detector 14.
Behind the subject M, an X-ray generator 3 that generates X-rays is attached to a telescopic support 15 hanging, for example, from the ceiling. The X-ray generator 3 is housed in a case 16. The case 16 houses an X-ray tube 17 and an X-ray restrictor 18. The X-ray tube 17 has a high voltage source (not shown). The height of the X-ray generator 3 can be adjusted to the subject M and the image receptor 4 by the telescopic mechanism of the support 15. Instead of hanging from the ceiling using the support 15, the case 16 can be supported by a support attached to the floor or the wall.
FIG. 14 schematically shows an X-ray radiographing apparatus for radiographing a subject M in the recumbent position on a bed. When radiographing such a subject M in the recumbent position, a moving image as well as still images of each part of the human body is often taken. A stereo image is constructed by processing a plurality of projection images. Various types of radiographing can be performed.
A support 21 supports a C-shaped arm 23 with a guide member 22 therebetween. At one end of the C-shaped arm 23 is the same image receptor 4 of FIG. 13, and at the other end is the same X-ray generator 3 of FIG. 13. The subject M is placed on a bed 25 disposed between the image receptor 4 and the X-ray generator 3 of the C-shaped arm 23.
In FIG. 14, the X-ray generator 3, the subject M, and the image receptor 4 are arranged in this order as in FIG. 13. The C-shaped arm 23 can be angled by a mechanism of the guide member 22. In an X-ray radiographing apparatus using a C-shaped arm 23, the positional relationship between the X-ray generator 3 and the image receptor 4 is fixed. Therefore, the process of adjusting the positional relationship is omissible. Therefore, this type of apparatus is convenient for radiographing in which the radiographing angle is frequently changed. However, the distance between the X-ray generator 3 and the image receptor 4 is difficult to change. Therefore, this type of apparatus is unfit for some types of radiographing.
The image receptor 4 can be used without being supported by any support. That is to say, the image receptor 4 can be used as a so-called electronic cassette. In this case, the image receptor 4 can be freely disposed above, for example, a bed, like a film cassette, and the degree of freedom of the positional relationship between the subject M and the image receptor 4 is increased.
As described above, according to the type of radiographing, the image receptor 4 is attached to an upright support or a C-shaped arm 23, or freely disposed as an electronic cassette. However, a radiographing apparatus including an X-ray detector using various types of image pickup devices and the maintenance cost thereof are expensive depending on the function and performance. Therefore, it is not economical for a facility to own many radiographing apparatuses corresponding to a wide variety of cases.
To solve this problem, an X-ray radiographing apparatus is widespread that has an X-ray detector that can be easily attached to and detached from a plurality of types of supports and therefore can be used in various types of radiographing. In addition, an X-ray radiographing apparatus is proposed that has an image receptor 4 that can detect X-rays without being supported by a support and can be used as an electronic cassette, like a film cassette, when detached from a support.
Further, although the purpose is different, a fitting locking mechanism is proposed that enables a case of an image receptor housing an X-ray detector to be attached to and detached from a coupler of a C-shaped arm. However, in the case of a support typified by a C-shaped arm that fixes the positional relationship between the X-ray generator 3 and the image receptor 4, the positional relationship between the X-ray irradiation axis and the X-ray detector needs to be sufficiently accurate. If the accuracy is insufficient, a favorable image may not be able to be obtained, and in addition, the surroundings of the area to be exposed may be needlessly exposed to X-rays.
The X-ray generator 3 is provided with an X-ray restrictor 18 for adjusting the area to be irradiated with X-rays. It is desirable that the shape and position of the X-ray restrictor 18 accurately correspond to the shape and position of the image reception area of the X-ray detector 14. In general, the image reception area of a solid-state flat detector is rectangular. In that case, the shape of the X-ray restrictor 18 needs to be a similar rectangle, and the position of the X-ray restrictor 18 in the direction of rotation around the X-ray irradiation axis is made to correspond to that of the image reception area of the X-ray detector 14. Therefore, when the image receptor 4 separated from a support is re-attached to the support, the image receptor 4 needs to be attached in the original position.
However, the X-ray detector 14 has a large projected area in a plane perpendicular to the X-ray irradiation axis, to ensure the necessary size for the detection area. In addition, to ensure the rigidity necessary to drive the X-ray detector 14 under favorable conditions, the case 13 of the image receptor 4 housing the X-ray detector 14 is liable to be heavy. The case 13 is difficult for the operator to lift. Sometimes the case 13 is difficult to attach in its correct position.
Even if a marker for position adjustment and fitting locking portions are provided, it takes time to find the marker for position adjustment depending on the position of the support and the position of the hand of the operator when lifting the case 13 of the image receptor 4.